Metrics  We adopt the widely-used BLEU [1]}, METEOR [2]}, ROUGE-L [3]} and CIDEr [4]}, which are calculated by the standard evaluation toolkit [5]}. In particular, BLEU [1]} and METEOR [2]} are originally proposed for machine translation evaluation. ROUGE-L [8]} is designed for measuring the quality of summaries. CIDEr [4]} is designed to evaluate image captioning systems.
